Hydraulic transmission



June 21, 1960 Filed July 23, 1957 Y F. E. CARLSON ETA!- HYDRAULICTRANSMISSION 5 Sheets-Sheet 1 June 21, 1960 F. E. CARLSON ETAL HYDRAULICTRANSMISSION 5 Sheets-Sheet 2 Filed July 23, 1957 June 21, 1960 F. E.CARLSON ETA!- HYDRAULIC TRANSMISSION s Sheeis-Sheet 3 Filed July 23,1957 F. E. CARLSON EIAL 2,941,365 HYDRAULIC TRANSMISSION 5 Sheets-Sheet4 June 21, 1960 Filed J lyzs, 1957 June 21, 1960 F. E. CARLSON ETAL2,941,365

HYDRAULIC TRANSMISSION Filed July 23, 1957 5 Sheets-Sheet 5 tates intentJr., Rockford, Ill., assignors to Sundstrand Corporation, acorporation'of Illinois FiledTuly 23, 1957, Ser, No; 673,666

35- Claims; (CL 60-'52) This invention relates to hydraulic systems, andmore particularly to hydraulic systems for mobile equipment of the slowmoving, hard working types, such as lift trucks and the like".

It is a general object of the invention to provide a new and improvedhydraulic system of the character de scribed. I 7

Vehicles of the type described, such as lift trucks, require drive meansfor propelling the vehicle, usually include a' lifting device such as alift fork, and require means for extending and retracting the liftfork", and means for raising and lowering the lift fork. Machines ofthis type require maneuverability in close quarters, precise and smoothoperation, the ability to withstand high shock loadsand overloads, andfrequent speed changes and reversals. 7

With the above and other considerations inniind; it is a more specificobject to provide a new and improved hydraulic system for propelling avehicle such as a lift truck, for extending and retracting a lift devicesuch as a lift fork, and for raising and lowering the lift device;

A further object of this invention is to provide a new and improvedhydraulic system of the type described in the preceding paragraphsincluding one or more motors for propelling the vehicle, a reach motorfor extending and retracting a lift device, a lift motor for raising andlowering the lift device, separately operable valves for the propelling,reach and lift motors respectively, connected in series circuit, andmeans providing a variable pressure, variable volume sourceoffiui'd'foreificiently supplying fluid under pressure only at the rateandpressure required for a particular operation.

Another object is to provide a new and improved by"- draulic system ofthe type described'in the preceding paragraph including a variablespeed, variable displace= ment pump, a prime mover for driving the ump,and a single control for controlling the speed of the prime. mover, thedisplacement of the pump, and the operation of the propelling, reach andlift valves;

It is also an object of the invention to provide a' new and improvedvariable pressure, variable volume hyice - 2 flow of fluid from themotor to thereby provide braking of the motor-.

Another object is to provide a new and improved transmission of the typedescribed in the'preceding para gra h including braking valve means forbraking the propelling motor on slowdown of the vehicle and when thevehicle is parked on an incline.

. A further object is to provide a new and improved transmission of thetype described including means for braking" the propellingmotor at anytime'when the" motor attains a speed requiring more flow than isdelivered to the motor, as may occur when a downward incline isencountered while operating at full speed.

It is also an object to provide a new and improved hydraulictransmission for propelling a vehicle of the type described including avariable displacement propelling motor, and means responsive to the loadimposed on the propelling motor for varying the displacement of thepropelling" motor to thereby vary the torque delivered by the motor inresponse to' variations in the loadon the motor. I K

A further object is to provide a new and improved hydraulic transmissionfor a lift truck or the like includ-' ing. a variable displacementpropelling motor, and manually operable means for varying thedisplacement of the motor between a" low speed, maximum torque value anddraulic transmission for propelling a vehicle of the type described.

A further object is to provide a new and improved transmission of thetype described inthepreceding paragraph including a variabledisplacement pump, a propela ling motor, a directional valve forcontrolling the flow of pressure fluid to the motor, and a singlecontrolfor simultaneously operating the directional valve and vary ingthe pump displacement.

Another object is to provide a new and unproven ny= draulic transmissionsystem for propelling avehicle of the type described including" at leastone propelling motor, means providing a source of operating fluid underpres sure, directional valve means for' controllingthe flow of pressurefluid to the'propelling motor, and valve means in the circuit with thepropelling motor to restrictthe a high speed, minimum torgue value.

Other objects and advantages will become readily apparent f'rom thefollovving" detailed description taken in connection with theaccompanying drawings, in which:

Fig; 1 is a hydraulic circuit diagram illustrating a hydraulictransmission system for a lifttruck or the like embodying the principlesof the present invention, showing the various elements of the system inneutral or normal positions; I P

Fig 2' is a hydraulic circuit" diagram illustrating a modified"hydraulic transmission system for alifttruck or the" like embodying theprinciples of the present invention, showing the various elementsinneutral or normal positions; a

Fig. 3 is a view of the system shown in Fi'g. 2; with the directionalvalve, the variable orifice, the pump control valve, and the automaticbraking valve shown in positio'ns dilferem from those illustrated inFig. 2';

Fig. 4 is a fragmentary view of the system shown in Fig; 3, showing theautomatic braking valve in a braking position;

Fig; 5" is another view of the system shown in Fig. 2, with theautomatic torque valve, andthe automatic prime mover control shown inpositions different from those illustratedin' Fig. 2; and

Fig. 6-is a hydraulic circuit diagram illustrating another modifiedhydraulic transmission system for a lift truck or the like embodying theprinciples of the present invention, with the various elements of thesystem positioned to'elfect reverse propelling ofthe lift truck at alow' speedunder control of the manually operable torque control valve.

While illustrative embodiments of the invention are shown in the"drawings and will be described in detail herein, the invention is'susceptible of embodiment in many difie'rent forms, and it should beunderstoodthat the present disclosure is to be considered as anexemplification of the principles of the invention and is not intendedtolimitthe invention to the embodiments inns trat'ed. The scope of theinvention will be pointed out in the appended claims.

The hydraulic system illustrated herein is particularly adapted for usewith mobile equipment of the slow movi'n'g, hard working type, suchaslift trucks and the like. Lift trucks of the type referred toconventionall include thereon a movably mounted lift device, such as alift 3 fork which is usually mounted for extension and retractionrelative to the lift truck to reach and to withdraw from the load. Thelift fork is also mounted for movement up and down on'the. lift truck tohoistand lower theload. A typical truck of the type referred to includesa truck chassis or frame, a pair ofdriving wheelssupported by one axleof the truck frame, usuallynear one end of the truck, one or moreguiding'wheels supported by the truck frame, usually near the other endof the truck, and means supporting the lift device-on the.truck framefor movement as described. The lift device .may comprise alift. fork ofgenerally L-shaped configuration includingafgen' erallyupright leg 'andagenerally horizontal leg,v the lat ter disposed for movement underneatha load, such as a pallet conventionally employed in warehouses and thelike for use in transporting stacked materials from place to place inthe warehouses by lift trucks of the character described. i

-The hydraulic system' in general The hydraulic system illustrated isadapted to be mounted entirely on the truck frame of a lift truck or thelike, and. includes means for propelling the truck, means for extendingand retracting the lift fork, and means for hoisting and lowering thefork. The system illustrated includes the advantages of a precise andsmooth control of each operation provided, with an unlimited speed rangefor each operation, and with a wide variation in torque for thepropelling operation. The system providesfor extreme flexibility ininstallation.

Referring nowto Fig. I particularly, as invention is embodied in asystem which includes a pair of hydrauliomotors and 11 adapted'forconnection respectively with a pair of driving wheels of the lift'truckfor propelling the truck. The motors 10 and 11 are of a variabledisplacement type inorder to provide a wide variation in developedtorque, and are reversible in order that the truck may be driven eitherforwardly or rever'sely. A third hydraulic motor 13 of a constantdisplacement type is provided for extending and retracting the lift forkto reach and [withdraw from'a load, and a fourth hydraulic motor '14, ofthe reciprocable piston and cylinder type, is provided for lifting andlowering the lift fork.

The system includes meansproviding a source of oper ating fluid underpressure, comprising a variable displacement pump 15 connected to besupplied from a reservoir 16 and adapted to be driven by a variablespeed prime mover 17, such as an internal combustion engine. The pump,the reservoir, and the prime mover are all adapted for mounting on thetruck frame and for suitable connection in the hydraulic system.Similarly, the hydraulic motors 10, 11, 13 and 14 are also adapted formounting on the truck frame, forsuitable connection in the hydraulicsystem, and for connection with the devices which they operate.

Operations of the propelling motors 10 and 11, the reach motor 13, andthe lift motor 14 are controlled respectively by 4-way directionalvalves, including a propelling valve -18, a reach valve 19, and a liftvalve which are connected in the systemto control the flow of operatingpressure fluid to and from the motors.

Operating fluid under pressure is supplied by the pump 15 to the body ofthe propelling valve 18 through a line 21a, 21b and 21c, and from thebody of the propelling valve 18 to the body of the reach valve 19, andfrom the body of the reach valve 19 to the body of the lift-valve 20.The valves 18, 19 and -20 are connected in series with the pump 15 andin series with each other. That is, when the valves are in neutralpositions as illustrated in Fig. 1, fluid from the pump 15 flows throughthe valves to the next adjacent valve downstream. When one of thevalves, the propelling valve :18 for example, is opera ated to directfluid to the associatedmotor, fluid under illustrated, the

pressure from the pump 15 no longer flows to the next valve downstream.Instead, the fluid flow from the propelling motors is directed to thedownstream valve. Fluid directed to the downstream valve in this mannermay be utilized by suitable actuation of the downstream valve to effectoperation of the associated motor. The respective motors are connectedin serieswith the associated directional valve. The motors may-beoperated separately, or

two or moreof them may be operated simultaneously. Whil'e'thedirectional valves have been illustrated as sep arate'structures, itwill' be appreciated that these may all be made, if desired, in a singlebody, or the three may be separate and-arranged in adjacent relationshipin a multiple unit valve stack. The propelling motors 1'0 and 11 areconnected in parallel with each other, and flow to these motors isnormally equally divided between the two motors so that the powersupplied thereto is the same. 7 1 Y Fluid under pressure flowing fromthe pump 15 passes through a member 22 providing an adjustable orificefor regulating the rate of flow to the directional valves. A pumpdisplacement control valve 23 is responsive to the pressure drop acrossthe adjustable orifice to vary the displacement of the pump 15 directlyas the rate of flow through the orifice varies. An overpressure reliefvalve 24 is responsive to pressure downstream of the adjustable orificeand functions in response to the development of v excessively high anddangerous system pressures to re-.

duce the pump displacement to a minimum.

A single manually operable control, generally designated 25 is providedfor controlling the operation of the directional valves 18, 19 and 20,and also for varying the size of the adjustable orifice and the speed ofthe prime mover 17. I

The propelling valve 18 includes valving described more in detailhereinafter, manually controllable, for obstructing the flow of fluidfrom the propelling motors 10 and 11 thereby to brake the motors whenthe lift truck is slowed down to a stop or when the truck is parked inneutral'on an incline. In order to facilitate the braking of thepropelling motors, the circuit connected with these motors includes abraking relief valve means 26 which functions to. maintain the brakingpressure, and to establish a' braking circuit returning braking fluidfrom the motor outlets to the motor inlets.

Also, the propelling motors circuit includes an automatic braking valvemeans 29 which functions to obstruct the flow of fluid from thepropelling motors and thereby brake the motors atany time when themotors require a flowgreater than that provided by the pump 15, as whenthe-motors tend to overrun at a time when the truck is on a downwardincline.

As previously noted, the propelling motors 10 and 11 areof the variabledisplacement type, and this characteristic is utilized to operate themotors either at a minimum displacement, high speed and low torque, orat a maximum displacement, low speed, and high torque. Operation of themotors in this fashion is controlled by an automatic torque valve means31 for controlling the displacement of the motors.

System in detail The pump 15 may be of a conventional constructionincluding a rotatable cylinder block 35 suitably keyed to a pump driveshaft 36 for rotation therewith. The cylinder block is formed with anannular series of axially disposed cylinders which receive thereinaxially reciprocal pump pistons 38 which are biased outwardly of thecylinder block by springs not visible. The pistons 38 through the mediumof suitable bearing shoe apparatus, bear against an adjustable angleswash plate 39 nonrotatably held in the pump housing 40. On rotation ofthe cylinder block' 35, in a conventional manner the pump cylinders drawfluid from aninlet conduit 41 leading from the reservoir 16 anddischarge fluid under. pres g sure into the pump outlet conduit 21apreviously referred to. A drain conduit 42 leads from the interior ofthe pump housing 40 to conduct leakage fluid to the inlet ine 41.

The variable angle swash plate 39 is normally biased to a minimumdisplacement position by means inherent in its mounting and by meansofthe spring biased pistons 38. Means is provided to vary the angle ofthe swash plate, and this means partaikes of a displacement varyingcontrol piston 46 mounted in a control cylinder 47 in the pump housingto bear against the swash plate 39. When the control cylinder 47 isconnected to drain, the swash plate 39 will assume aminimum-displacementposition. Control fluid under pressure may be admitted to the cylinder47 to increase the swash plate angle "and thereby increase the pumpdisplacement.

The control valve means 23, previously referredto, is provided tocontrol the flow of pressure fluid to and from the cylinder 47 inresponse to variations in the ilow rate through the adjustable orificein the member 22. The control valve 23 functions to effect an increasein 'pump displacement on increased flow through the orifice and toeffect a decrease in pump displacement on decrease in the flow ratethrough the orifice.

The control valve 23 includes a valve body 51 which desirably may beintegral with the pump housing end plate a. The valve body 51 is formedwith a bore having a valve member 52 slidably positioned therein. Thevalve member 52 is biased by a spring 53 toward 'a position establishingcommunication between an outer groove 55 on the valve member and a valveport 56 in the valve body. Radial passages 57 formed in the valve member52 communicate with the groove 55 and lead to an axial passage 58 in thevalve member which opens to "the lower end of the valve member tocommunicate with a valve inlet port 59. An outer annular groove 60formed on the valve member 52 is provided to establish communicationbetween the valve control port 56 and a drain port 61 when the valvemember 52 is positioned as illustrated in Fig. 1.

Valve member 52 is sensitive to the pressure drop across the adjustableorifice in the member 22. 'Its upper end is exposed to pressure fluidahead of the adjustable orifice by means of conduits 62 and 63 whichlead from the pressure conduit 21a to the upper end of the valve body51. The lower end-of the valve member 52 is subjected to pressure fluiddownstream of the adjustable orifice through the medium of conduits 64,65 and 66, which lead from the pressure conduit 210 to the'valve inletport 59.

In operation, when the adjustable orifice is closed or substantiallyclosed, there-will be a pronounced pressure drop across the orifice, andthe pressure of fluid in the lines 210, 62 and 63 will be much greaterthan the pressure of fluid in the conduits 21b, 21c, 64, 65 and 66. As aresult of this pressure difi'erential, the greater pressure at the upperend of the valve member 52 will force the valve member downwardlyagainst the bias of the spring 53 to substantially the positionillustrated in Fig. 1. In this position of the valve member, the controlcylinder 47 is connected to drain by means of a conduit 67 which leadsfrom the control cylinder to the overpressure relief valve 24, theoverpressure relief valve,'a conduit 68, the port 56, the groove 60, andthe drain port 61 which is connected by conduit 70 to the interior ofthe pump housing 40.

In the event the adjustable orifice is opened to' permit an increasedflow rate therethrough, the pressure drop across the orifice will besubstantially reduced, the pressure acting against the lower end of thevalve member 52 will be increased, and such pressure and the spring 53will be effective to move the valve member 52 upwardly to a positionestablishing communication between the pressure conduit 66 and thecontrol cylinder 47 through the axial passage 58, the :radial passages:57,

splices ,6 groove 55, control port 56, conduit 68, relief valve 24, andconduit 67. The position of the valve member just described is notillustrated in connection withthe circuit of Fig. l, but is illustratedin the modified circuit of Fig. 3 wherein the control valve isdesignated 23x. In this position of the control valve, pressure fluidacting against the control piston 46 will be elfective'to increase theangle of the Wobbler 39, thereby increasing the pump displacement inproportion to the flow rate 'through'the adjustable orifice.

The overpressure reliefvalve 24 "includes a valve body '72 which alsomay be formed integrally with the pump housing end plate 15a. The valve.body 72 is formed with the bore having a valve member 73 slidablypositioned therein and normally biased upwardly by a spring 74- to theposition illustrated in Fig. 1 wherein an outer annular groove 75 formedon the valve member places the two conduits 67 and 68 in communicationso that control over the control piston 46 is maintained by the controlvalve 23. The upper end of the valve member 73 is subjected to fluidunder pressure from the conduit 2112. In the event that an excessivelyhigh "and dangerouspressure is developed in the system, as may occurwhen a passage is improperly blocked or a part improperly jammed, suchpressure functions to move the valve member 73 downwardly to a position(not illustrated) wherein an outer annular groove 76 on the valve membercommunicates with the conduit 67. When the valve member is thuspositioned, the control cylinder 47 is connected to drain throughtheconduit 67, the groove 76, radial passages 77, an axial passage 78,and a conduit 79 leading to the drain conduit 70. The swash plate 39 isthereby allowed to return to a minimum displacement position to reducethe pump output until such time as the defective conditionin the circuitis corrected.

The adjustable orifice .in the member 22 is formed by means including avalve body 81 formed with a bore 82 having an inlet port 83 and anoutlet port 84. The outlet port 84.forms an annular valve seat forcooperation with the conical end portion of a valve member rotatable andslidable in the bore 82. The valve member '85 is formed with a threadedend portion 38 which is screwed into the valve body -81. Adjustment ofthe size of the orifice opening formed by the outlet port 84 and theconical end portion of the valve member is obtained by rotating thevalve member 85 to screw the latter inwardly and outwardly relative tothe outlet port '84. Rotation of the valve member 85 is effected bymeans of a rotatable shaft 36 mounted in a suitable bearing 87 andadapted to be rotated under control of the manually operable con trol25.

The pump drive shaft 36 is connected to be driven by the prime mover 17which may comprise an internal combustion engine of a conventional typehaving an output shaft 90 suitably connected to drive the pump shaft 36.The speed of the engine 17 is controlled by a fuel feed device such as acarburetor 91. The carburetor is controlled by a mechanism including apivotally mounted lever 92 normally biased by a leaf. spring 93 againstan adjustable stop 94 so as to normally supply sutficient fuel .to theengine 17 to sustain its-operation at an idle speed.

The carburetor control lever 92 is connected to be automaticallycontrolled with adjustments in the size of the orifice 22 by means of alink 95 pivotally connected at one end to the lever 92 and at .its otherend to an eccentric pin 96 on a .disc 97 secured to the adjustment shaft86 for rotation therewith.

In operation, when the adjustable valve member 85 is positioned asillustrated in Fig. 1 to substantially close .the valve outlet 84, theeccentric pin 96 and the link 95 are positioned to adjust the carburetorto an idle speed. On rotation of the adjustment shaft 86 to increase thesize of the orifice opening 22, the eccentric pin 96 is revolved aboutthe axis of the shaft 86, :mov- .ing the connecting link 95 to the leftas viewed inFig. l,

to. increase the fuel feed to the engine 17 and thereby increase thespeed of the engine with increases in the flow .rate through theadjustable orifice.

Rotation o'f-the adjustment shaft 86 is effected by the single commoncontrol device which is provided to effect operation of all manualcontrols included in the sysstem. The control 25 includes a supportingbracket having a centrally disposed hub portion 101 which supports arotatable shaft 102. The shaft 102 is connected by a flexible shaft 103to the adjustment shaft 86. The drive shaft 102, at its other end,supports an operating ;lever 104 universally connected with the driveshaft 102 at 105 and having a manually accessible hand grip portion froma neutral center position illustrated in Fig. l for purposes describedmore fully hereinafter. Also, however, the hand grip portion may beutilized to rotate the operating lever 104 about its axis, thereby torotate the drive shaft 102 for effecting adjustment of the adjustableorifice in the member 22 and for varying the speed of the prime moverengine 17.

As previously noted, when the adjustable orifice is opened, operatingfluid under pressure flows from the bore for movement in oppositedirections from the neutral center position illustrated in Fig. 1.

The valve body is formed with a pairof inlet ports 113 and 114, bothcommunicating with the pressure conduit 21c and both adapted tocommunicate with the valve bore 111. The valve body 110 is also formedwith a pair of motor ports 115 and 116 for delivering pressure fluid toconduits 117 and 118 respectively to obtain operation of the propellingmotors 10 and 11 in reverse and forward directions. Motor ports 119 and120 in the valve body communicate respectively with the conduits 117 and118 for returning fluid from the propelling motors 10 and 11 when themotors are operated in forward and reverse directions. Drain ports 121and 122 in the valve body 110 are both connected with a drain conduit123 leading to the braking valve 29. The braking valve includes anoutlet port 124 communicating with a pair of inlet ports to thedownstream directional valve 19.

The propelling motors 10 and 11 are connected in series with thepropelling valve 18 and in parallel with each other by means includingthe conduit 118 and branch conduits 125 and 126 which conduct operatingfluid under pressure to the motors for operating the motors in a for-Ward direction. The conduit 117 and branch conduits 127 and 128 conductoperatingfluid under pressure to the motors for obtaining operation in areverse direction. It will be understood that the circuits described,connecting the motors in parallel with each other provide for adifferential action which permits relative movement between the motorsas when the lift truck is turning with the wheel connected to one motortraveling in an arc of greater radius than the wheel connected to theother motor.

In operation, when the valve stem 112 of the valve 18 is positioned inthe neutral center position as illustrated in Fig. l, fluid flows fromthe conduit 21c to both valve in let ports 113 and 114. From the inletport 113, fluid flows through stem groove 129 to the drain port 121 andto drain conduit 123. From the inlet port 114, fluid flows through thestem groove 130 to the drain port 122 and to drain conduit 123. I

In order to obtainoperation of the propelling motors in a forwarddirection, the valve stem 112 is moved upwardly from the positionillustrated in Fig. l to a position wherein the inlet port 113 isblocked by valve land 131. The entire flow from conduit 21c passes tothe propelling motors through valve inlet port 114, stem groove 130,motor port 116 and conduit-118. Valve land 132 is positionedto block themotor return port 120 and the drainvtion 106 for pivoting the operatinglever 104 in any direc- 8 port 122. When the valve is positioned asdescribed, fluid flows from the motors 10 and 11 to drain through con;duit 117, motor return port 119, stem groove 129, drain port 121, anddrain conduit 123. The valve land 131 is positioned to block the motorport 115. The position of the valve just described is not illustrated.

groove 129 motor port 115, and conduit 11 7 The valve land 133 ispositioned to block the motor return port 119 and the drain port 121.When the valve is positioned as described, return flow from the motors10 and 11 passes through conduit 118, motor port 120, stem groove 130,drain port 122'and drain conduit 123. The motor port 116 is blocked byvalve land 131. The position of the valve just described isnotillustrated in Fig. 1, but is illustrated in the modified circuit ofFig. 6.

Movement of the valve stem 112 from the neutral center positionillustrated to the positions described is effected by means to bedescribed presently.

The manually controllable valve 18 for controlling operat-ion of thepropelling motors 10 and 11 includes valving for braking the propellingmotors on slow down and in neutral. Principally, the valving referred tocomprises the lands 131, 132 and 133 on the valve stem 112. When thevalve stem 112 is positioned as illustrated in Fig. l, the lands 131 and133 are positioned to bloclcthe flow of fluid from the motor conduit117, and

the lands 131 and 133 are positioned to block the flow of fluid from themotor conduit 118. If the lift truck is parked on an incline, facingeither forwardly or -reversely, the weight of the truck and the loadcarried thereby will tend to cause the truck to roll down the ramp. Suchcondition causes the propelling motors 10 and 11 to function as pumps.But, inasmuch as both motor conduits 117 and 118 are blocked, thepropelling motors, when rotated in either direction, pump against ablocked passage. Obviously, this restricts the flow of fluid from themotors, and brakes the motors.

The braking relief valve means 26, previously referred to in general, isprovided to maintain the braking pressure in the motor return line 117or 118, depending on the direction of truck movement. This valve meansfunctions to bypass fluid from the motor return line to the motor inletline to regulate the braking pressure in the return line and at the sametime maintain hydraulic fluid in the braking circuit.

The braking relief valve means 26 includes a valve body 135 having afirst conduit 13 6 connected to the motor conduit 117 and a secondconduit 137 connected with the motor conduit 118. The valve body 135 isalso provided with two valve bores, one bore housing a spring pressedcheck valve 138 biased to a closed position against the pressure offluid in the conduit 136. The

second bore houses a spring pressed check valve 139 biased to a closedposition against the pressure of fluid in the conduit 137. Passagesprovided in the valve body enable the valve 138 to deliver fluid fromthe conduit 13 6 to the conduit 137 and additional passages enable thevalve 139 todeliver fluid from the conduit 137 to the conduit 136.

In operation, assuming the truck is parked in neutral, as illustratedinFig. l, on an incline such that the truck tends to roll forwardly, themotors 10 and 11 tend to .function as pumps, drawing fluid in throughthe motor conduit 118 and pumping the fluid out through the conduit 117.In this case, the valve lands in the valve 18 block the flow of fluidfrom the motors. The valve 138 is biased toward a closed position by itsspring, and will thus maintain the braking pressure in the line 117 upto a predetermined value, at which time the valve. open.

. Q 'Wheii the valve opens, the motor outlet line117 is connected to themotor inlet line 118 to thereby return fluid to the motor inlets. Thevalve 138 thus functions to regulate braking pressure and to provide abraking circuit and to maintain the braking circuit charged with fluid.The braking relief valve 139 functions in a similar manner when thetruck tends to roll rearwardly and the propelling motors thus tend topump out the conduit 118 and draw through the conduit 117. The settingof the valves 138 and 139 may be high enough so that they do not relievethe pressure of fluid for propelling the truck when the valve stem 112is positioned for this purpose.

The automatic braking valve means 29, previously referred to in general,includes a valve body 141 having an inlet port connected with the drainconduit 123 and an outlet port 124 previously described. The valve body141 is formed with a valve bore having a valve member '142 slidablydisposed in the bore and formed with a central reduced portion 143 whichserves to connect the valve inlet port 123 and the valve outlet port 124when the valve member is positioned as illustrated in Fig.1. A spring144 acts against the valve member 142, biasing the valve toward aposition in which communication is blocked between the inlet port 123and the outlet port 124. At the opposite end of the valve member fromthe spring 144, the valve boreis provided with a pressure port 145 whichis connected by a conduit 14 6 with the pressure conduit 64, and hencewith conduit 21c, leading from the source of pressure fluid.

In operation, at any tune when the pump 15 is pumping, and theadjustable orifice in member 22 is open, the pressure of fluid in theconduit 14-6 is su'flicient to maintain the valve member 142 in aposition as illustrated in Fig. 1, thereby placing the inlet port 123andthe outlet port 124 in communication. Thus, under normal operatingconditions, when the propelling motors 1i and 11 are operated eitherforwardly or reversely, at either high speed or low speed, the returnconduits from the motors are opened to drain since the valve member 142is positioned to interconnect the drain ports 123 and 124.

If, under these conditions, the truck encounters a downward incline, themotors and 11 may tend to overrun at a speed requiring more flow throughthe motors than is delivered by the pressure source. In this case, themotors begin to function as pumps, drawing fluid from the pressureconduit 21c and pumping through the drain port 123. Since the propellingmotors are functioning as pumps and are requiring more lluid than thatdelivered by the pressure source, the pressure of fluid in the pressureconduits 21c and 146 drops, enabling the spring 144 to move the valvemember 142 to a position blocking communication between the ports 123and 124. Since the flow of fluid from the motors 11 and 11 is therebyrestricted, the motors are braked down to a suitable speed, after whichthe pressure of the operating fiuidwill rise again to the proper value,again opening the braking valve 29. The braking position of the valvemember 142 has not been illustrated in connection with the circuit ofFig. 1. However, the braking position of a similar braking valve isillustrated in Fig. 4 in connection with the illustration of the circuitof Figs. 2 through 5.

The propelling motors 10 and 11 may be similar and of conventionalconstruction. Since the motors shown are identical, only motor 10 willbe described in detail.

pelling motors is utilized, in combination with the torque actressmultiplication valve means 31, previously referred 'to irl general, .toobtain the optimum usage of a small mover, enabling the reduction inover-all size of a lift truck or the like where maneuverability in closequarters is essential. With the hydraulic system illustrated, theoptimum size prime mover, such as the engine 17, is one that willprovide just enough power to maintain thevehicle at full speed with afull load on a level surface with no reserve power to climb an inclineor ramp. The automatic torque multiplication valve 31 enables thepractical use of a small prime mover engine by automatically sensing anoverload condition on the motors 10 and 11 to automatically increase thedisplacement of the motors, thereby providing an increased torque outputand a reduction of the speed of the motors.

As illustrated, the torque multiplication valve includes a valve body157 having a pressure port 158, a control port 159 and a drain port 160.The valve body 157 is formed with a valve bore having a valve member 161slidably positioned therein. The valve member is normally biased to theposition illustrated in Fig. 1 bya spring 162, in which position anexternal annular stem groove or reduced portion 163 on the valve memberconmeets the control port 159 and the drain port 160. When thevalve'mem-ber 161 is positioned as illustrated, the control pistons forthe motors 10 and 11 are con nected to drain through the drain port 160,the stem groove 163, the control port 159, a conduit 164 leading fromthe control port 159, and branch conduits 165 and Y166 which lead to thecontrol pistons 155. The variable angle swash plates 154 for the motors10 and 11 are thereby permitted to assume their normal minimumdisplacement angle for etfecting operation of the motors at a high speedand a low torque.

The valve body 157 is formed with an additional port 167 connected by aconduit 168 to the pressure conduit 66. The valve member is therebyexposed to pressure fluid. In operation, the valve member 161 isnormally positioned as illustrated in Fig. 1. In the event that thepropelling motors 10 and 11 encounter an undueresisb ance to turning, aswhen the wheels driven thereby en counter an obstruction or an incline,the increased resistance to turning causes a pressure rise in thepressure conduits 66 and 168. The increased pressure causes movement ofthe valve member 161 to a position wherein the pressure .port 158 andthe control port 159 are cortnected through the reduced portion 163.Pressurefiuid is thus supplied to the conduit 164 and branch conduits165 and 166 to actuate the control pistons 155 and 155" shifting theswash plates 154 and 154' to an increased angle providing increasedmotor displacement, increased torque at the motors, and reduced speed.If the resistance of the motors 10 and 11 to turn decreases, there willbe a pressure drop in the system which permits return of the valvemember 161 to the position illustrated, thereby connecting the controlpistons to drain. This permits return of the swash plates to minimumdisplacement angle. The shifted position of the torque multiplying valvemember 161 referred to above is illustrated in .Fig. 5, wherein thetorque valve is generally designated 31x.

If desired, the circuit illustrated in Fig. 1 may incorporate a manuallyoperable torque n-iultiplication valve similar to that described inconnection with the circuit illustrated in Fig. 6. p

The directional valve. 19 for controlling the flow of operating fluid tothe reach motor 13 is substantially identical with the directional valve'18 for controlling the flow to the propelling motors Ill and 11. Forthis reason, the valve 19 will not be described detail. The parts of thevalve referred to in describing its operation have been given referencenumbers similar to the correspending parts of the valve 18, with a primeadded. I

The reach motor 13 may be of a conventional type including a rotatablecylinder block 170 connected to amass ,drive an output shaft 171 andhaving axially reciprocal pistons 172 bearing against a swash plate 120having a fixed angle for providing a constant piston displacement. The.construction of the motor 13 is such that it may be operated forwardlyor reversely by reversing the direction of fluid flow through the motor.

1,: n operation, when the valve stem 112 of the directional valve 19 ispositioned as illustrated in Fig. 1, fluid flows from the inlet ports113' and 114' to the drain ports 121 and 122' through the stem grooves129' and 130'. With the valve positioned as illustrated, the motor ports1 116, 119, and 120' are blocked by the valve lands 131', 132' and 133'.

Operation of the reach motor forwardly is obtained by moving the valvestem 112 upwardly from the neutral center position illustrated to aposition in which the stem' groove 130 connects the inlet port 114' tothe motor 'pressure port 116' to deliver operating fluid through theconduit 118 to the reach motor inlet. Operation of the reach motorreversely may be obtained by moving the valve stem 112' downwardly fromthe position illustrated to a position in which the stem groove 129'connects the :motor inlet 113' to the motor pressure port 115' todeliver operating fluid under pressure through the conduit 117' to themotor 13.

Movement of the valve stem 112 is effected by means to be describedpresently.

The directional valve for controlling operation of the lift motor 14 issubstantially identical with the valves 18 and 19 previously described.Accordingly, the valve 120 will not be described in detail. The :partsof the valve referred to in describing its operation have been givenreference numbers similar to those given to corresponding parts in thevalves 18 and 19, except that a double prime sufiix has been added. Thelift motor 14 may be of a conventional piston and cylinder typeincluding a cylinder 175 having a pisjton 176 reciprocable therein andhaving -a piston rod 177 adapted to be connected with the lift fork ofthe lift truck.

Fluid is admitted to the cylinder 175 to elevate the lift fork throughmotor pressure port 115", a check valve 184, and a conduit 178 leadingto a cylinder port 179. Fluid is exhausted from the cylinder 175 tolower the lift fork through the conduit 1.78 and the motor drain port119". The lowering of the lift fork may be accomplished at a ratecontrolled by an adjustable metering .valve or the like 180 located in adrain conduit 181 leading from the drain port 121 to a drain conduit 182con 'nected with the reservoir 16. A conduit 183 leads from the valvedrain port 122" to the drain conduit 182. .Since operation :of the liftmotor 14 requires the flow of fluid to and from only one end of thecylinder 175, the

motor ports 116" and 120" may be connected by a'closed loonduit or, ifdesired, plugged, or eliminated entirely.

'In operation, when the valve member 1 12" is positioned in the neutralcenter position as illustrated in Fig. 1, "fluid enters the valvethrough the inlet ports 113" and 114", passes through the stem grooves129" and 130", drain ports 121" and 122", conduits 181 and 183', andconduit 182 to the reservoir 16. With the valve stem positioned asillustrated, the motor ports119" and 115" are blocked by the valve lands133" and 131" so that ,the piston 176 is effectively held in position tohold a load.

' In order to effect movement of the lift piston upwardly, "the valvestem 112" is moved downwardly from the position illustrated to aposition in which the stem groove I129" connects the inlet port 113"with the motor pressure port 115". In this position of the valve stem,the motor port 119' is blocked by the valve land 133". In order topermit movement of the lift piston 176 downwardly, the valve stem 112"is moved upwardly from the position iillustrated to a position in whichthe stem groove 129" connects the motor return port 119" to the drainport 121". In this position of the valve stem, fluid flows from thecylinder 175 at a rate controlled by the adjust- 1-2 able valve tocontrol the rate at which the lift fork is lowered. Movement of thevalve stem 112' is effected by means which will be described now.

The valve stem 112 in the directional valve 18 is biased to the neutralcenter position illustrated in Fig. 1 by means of a spring 185. Thespring bears against a lower collar 186 and an upper collar 187, bothslidable on a reduced portion of the valve stem 112 in an enlargedportion of the valve body bore 111. The collars 186 and 187 are bothadapted to bear against shoulders formed on the valve stem and in thevalve bore in a manner to permit movement of the valve stem in oppositedirections from the neutral center position shown to the two operativepositions previously described. A collar 188 fixed on the reducedportion of the valve stem is engageable alternatively with the collar186 or the collar 187 to limit movement of the valve stem 112 inopposite directions.

he valve stems 112' and 112" of the directional valves 19 and 20 arenormally biased to the neutral center positions illustrated by meansidentical with that described in connection with the valve stem 112.

Movement of the valve stem 112 in the directional valve 18 upwardly fromthe position illustratedin Fig. 1 is effected by the admission ofpressure fluid to a cylinder 190 formed at the lower end of the valvebody 110. Fluid under pressure is admitted to the cylinder 190 through aconduit 191 leading from the cylinder to a control valve 192. Movementof the valve stem 112 downwardly from the position illustrated in Fig. 1is effected by admission of pressure fluid to a cylinder 193 formed inthe upper end of the valve bore 111. Pressure fluid is admitted to thecylinder 193 through a conduit 194 firom'a control valve 195.

The pilot control valves 192 and 195 for controlling operation of thevalve stem 112, together with similar pilot control valves 192' and 195'for controlling opera- 'upper central portion of the figure, inelevation for illustrating the mechanical features of the unitpreviously described hereinabove. The master control 25 has beenillustrated in Fig. 1 a second time at the upper right hand portion ofthe figure where the unit is shown in section, the sect-ion being takenthrough the pilot control valves 192 and 195 for illustrating thehydraulic features of the unit about to be described.

The stationarily mounted supporting bracket 100 of the control unit 25includes four leg portions 197 which are angularly spaced about the axisof the drive shaft 102 and extend from the hub portion 101 axially andradially outwardly. The leg portions 197 provide supports for the valves192, 195, 192' and 195, which are spaced at 9.0 degree intervals aboutthe axis of the manually operable control member 104 when the latter ispositioned in the neutral center position illustrated.

The pilot control valves 192, 195, 192/and 195' are identical inconstruction. Hence, only the valve 192 will be described in detail; theconstruction of the remaining valves will be understood from thedescription of the valve 192.

The valve 192 includes a valve body 200 formed with a valve bore havinga pressure port 201, motor port 202,

and a drain passage 203 through the valve body intersecting the valvebore. The valve bore receives a slidably mounted valve stem 204 which isbiased by a spring 209 .to the position illustrated wherein a stemgroove 205 13 port 202, stem groove 205, and drain passage 203. When thevalve member 204 is positioned as illustrated, a reduced end portion 206on the valve stem bears against the universally pivotable control lever104.

In like manner, the similar valves 195, 192 and 195' are similarlypositionedto connect the cylinders 193, 190', and 193' to drain. Thedrain passages of the four valves are interconnected as shown by aconduit 207 which in turn is connected to a conduit 208 leadingto thedrain passage 182.

Operating fluid under pressure is delivered to the pilot control valvepressure port 201 by means of a conduit 210 which leads from thepressure conduit 62, a connecting conduit 211, and a conduit 212. Thepressure port of the valve 195 is supplied with pressure fluid throughthe conduit 210, and a connecting conduit 213 which leads to thepressure port of the valve 195.

Pressure fluid is supplied to the pressure port of the pilot valve 192'through the conduit 210 and a connecting conduit 214. Pressure fluid issupplied to the pressure port of the valve 195 through the conduits 210,211, and a connecting conduit 215.

-In operation, when the valves 192, 195, 192' and 195 are positioned asillustrated, the cylinders 190, 193, 190' and 193' are each connected todrain, and the control valve stems 1:12 and 112" are biased by thesprings 185 and 185 to the neutral center positions illustrated.

In order to effect movement of the valve stem 112 upwardly from theposition illustrated to the position previously described for obtainingforward operation of the propelling motors and 11, the pilot valve 192is actuated to conduct pressure fiuid to the cylinder 190. Actuation ofthe pilot valve 192 is effected by pivotal movement of the control lever104 upwardly from the position illustrated in Fig. l to move the pilotvalve stem 204 from the position illustrated to a position in which thestern groove 205 connects the pressure port 201 and the motor port 202.When the stem 204 is moved to the position described, pressure fluid isdelivered to the cylinder 190 through the conduit 191 to effect movementof the valve stem 112 upwardly.

In order to effect movement of the valve stem 112 downwardly from theposition illustrated to the position previously described for obtainingoperation of the propelling motors 10 and 11 reversely, the pilot valve195 is actuated to admit pressure fluid to the cylinder 193. Actuationof the pilot valve 195 is effected by movement of the control lever 104downwardly from the position illustrated to a position in which thepilot valve stem groove connects the pressure conduit 213 and theconduit 194.

In similar fashion, movement of the valve stem 112 downwardly to theposition previously described to effect movement of the lift piston 176upwardly, is effected by actuation of the pilot valve 195', by thecontrol lever 104 to connect the pressure conduit 215 and the conduit194'. Movement of the valve stem 112" upwardly from the positionillustrated to the position described for lowering the lift piston 176is effected by actuation of the pilot valve 192' by the control lever104 to connect the pressure conduit 214 and conduit 191 for admittingpressure fluid to the cylinder 190".

Thus, it will be seen that the control lever 104, in addition toproviding an adjustment for the variable orifice 22 and an adjustmentfor varying the speed of the prime mover 17, also provides a singlecontrol for effecting operation of the directional valves 18 and 20. Asexplained, any one of the four pilot valves may be actuated by pivotalmovement of the control lever 104 in the proper direction. Additionally,actuation of any two adjacent pilot valves may be effectedsimultaneously by moving the control lever 104 in an angular directiontoward both adjacent pilot valves. More specifically, the control lever104 may be moved upwardly and leftwardly at a 45 degree angle to actuatethe valve 192 and the valve 'to simultaneously obtain forward propellingmovement of the truck and hoisting movement of thelift device.

Movement of the valve stem. 112' upwardly and downwardly from theneutral-center position illustrated to the two positions previouslydescribed is effected by means of solenoids. A solenoid 217 is providedto move the valve stem 112 downwardly and the solenoid 218 is providedfor moving the stern upwardly. The solenoid 217 is connected to groundand to a source of power represented at 219 by means of a wire 220througha switching device 221 on the control lever 104 which includes apush button switch actuator 222 for energizing and deenergizing thesolenoid. The solenoid 218 is connected to ground and to the source ofpower by a Wire 223 through switching device 221 which also includes apush button switch actuator 224 for controlling energization of thesolenoid 218. The switching device 221 including a push button switchactuator 222 and 224 may be of a conventional construction, and ismounted on the control lever 104 so as to permit control of the valve19, as well as the other controls previously described, all from asingle control device.

Modified circuit The modified circuit of Figs. 2 through 5, like the (incuit of Fig. 1, is a variable volume, variable pressure system.

A principal difference in the modified circuit resides in the provisionof an adjustable flow rate orifice in the pump discharge line which isincorporated in the directional valve for controlling operation of thepropelling motors. In the previously described circuit of Fig. l theadjustable orifice is completely separate and apart from the directionalvalves, and although adjustable by a control member also utilized tocontrol operation of the directional valves, a separate movement of thecontrol member is required to adjust the variable orifice differing fromthe movement of the control member to adjust the directional valves.

In the modified circuit of Figs. 2-5, wherein the adjustable orifice ismade a part of the directional valve, the orifice opening and thedirectional valve opening are both controlled by a single valve member.Thus, as the directional valve is opened, the orifice is openedproportionately, to automatically increase the pump output in conformitywith the position of the directional valve stem and control handle.

Also, in the modified circuit of Figs. 2-5, means is provided to varythe prime mover engine speed automatically in response to variations inthe fluid pressure in the pump discharge line. In the system of Fig. 1,engine speed is controlled manually with adjustment of the variableorifice. With automatic control of the engine speed as in the circuit ofFigs. 2-5, the speed varies with the load on the system.

Another important advantage in the system of Figs. 2-5 resides in theprovision of makeup valve means and makeup porting in the directionalValve stem which function when the directional valve is positioned inneutral to provide makeup fluid, replacing leakage, to maintain thebraking circuit charged with fluid.

A principal advantage of a variable volume, variable pressure system ofthe type shown in all the drawings is that it provides a most eflicientmeans of propelling .a lift truck or the like, because the systemprovides operating fluid only at a rate and a pressure required for anygiven operating condition. While variable volume, variable pressuresystems can be utilized for obtaining other functions than propelling,precise and independent control of the speed of several operations atonce is difficult to obtain. The modified circuit of Figs. 2-5advantageously includes only propelling motors, With no reach or liftmotors for operating a lift fork or the like included in the system.

Thus, the modified circuit illustrated in Figs. 2 through 5 embodiesprinciples similar to those incorporated in the system of Fig. 1, andalso includes some features which differ from the system of Fig. 1.Elements of the modified system which correspond to the system of Fig.ili have been given similar reference numbers with a suf- Generally, thesystem of Fig. 2 includes the variable displacement propelling motors102: and 11x adapted to be connected to the driving wheels of a lifttruck or the like, a variable displacement pump 15x for supplyingoperating fluid from a reservoir 16x, and connected to be driven by aprime mover 17x, all of which may be identical with the correspondingelements in the system of Fig. l. The flow of operating fluid underpressure from the pump 15x through a delivery line 21x to the propellingmotors is controlled by a directional valve 18x. Operation of thevariable displacement pump 15x is controlled by a displacement controlvalve 23x and an over pressure relief valve 24x which may be identicalrespectively in construction and operation with the control valve 23 andthe over pressure relief valve 24 illustrated in Fig. 1.

As in Fig. 1, the directional valve 18x includes braking valving torestrict the flow. of fluid from the propelling motors when the valve ispositioned in neutral, as illustrated in Fig. 2. The system of Fig. 2includes a braking relief valve 26x which may be identical with thebraking relief valve means 26 in Fig.1, for operation in conjunc- 'tionwith the braking valving referred to to maintain pressure on the brakingcircuit and to port braking fluid from the motor outlets to the motorinlets. The system of Fig. 2 includes automatic brake valve means 29xsimilar to the brake valve 29 in the system of Fig. 1, except that thestem groove 143x in Fig. 2 is tapered, as illustrated, to provide agradual cut off at the port 123x.

The system of Fig. 2 includes an automatic torque multiplication valve31x similar to the valve means 31 in Fig. 1, for controlling thedisplacement ofthe propelling motors x and 11x to automatically increasethe torque output of the motors and vary their speed inversely'inresponse to pressure rises in the system due. to increased load onthemotors. In the system of Fig. 2, the torque valve is subjected topressure fluid at the port 167x ahead "of the variable orifice 22x,instead of downstream from 'the orifice as in Fig. 1. This differenceisof little significance, however,.since the pressure above and belowthe variable orifice is substantially the same when the orifice is fullyopened, and it is only when the orifice is opened that the torque valveis intended to function.-

16 250, 251, 252, and 253. Movement of the valve stem 235 is obtained bymeans of a manually operable lever 255 pivotally mounted on the valvebody and having a suitable pin and slot connection with the valve stem.

The variable orifice 22x is formed in the-system of Fig. 2 by meansincorporated in the directional valve 18x in- ,cluding the valve inletgroove 237 and the central valve land 247 which is tapered at oppositeends in order to obtain a gradual opening and closing of the orifice. 7When the valve stem 235 is positioned as illustrated in Fig. 2, theorifice 22x is completely closed, there is no flow to the propellingmotors, and the pressure upstream from the orifice builds up to a valueconsiderably greater than that in the conduit 24! downstream of theorifice, and the upstream pressure is sufficient to move the controlvalve 23x to the position illustrated in Fig. 2 wherein the valveconnects the pump control conduit 67x to drain and the pump assumes aminimum displacement operation.

In the system of Fig. 2, braking on slow down and while the truck isparked in neutral on an incline occurs in much the same manner as inthesystem of Fig. 1. With the valve stem 235 in neutral, as illustratedin Fig. 2, the motor po'rts 241 and 242 are blocked by the valve lands.249 and 248 so that there is no flow to or from the motor. If the valvestem is moved to the neutral position from an operating position to slowthe truck down to a stop, or if the truck is parked in neutral on anincline, the motors 10x and 11x will tend to turn and to function aspumps. However, as illustrated, the motors pump against the closeddirectional valve 18.x, and the latter thus functions to brake themotors. On continued rotation of the motors, braking fluid is pumpedthrough one of the braking relief valves 138x or 139x, depending on thedirection of rotation, in the manner described in connection with thedescription of the system of Fig. l. The braking relief valve meansfunctions to maintain pressure on the braking fluid in the motor outletlines, to relieve this pressure to the motor inlet lines, therebyproviding a braking circuit and maintaining the circuit charged withfluid.

During the braking operation described, it may be necessary to chargethe braking circuit with makeup fluid because of leakage which may tendto dissipate the braking fluid. To this end, makeup valve means 230 ispro-.

vided to deliver makeup fluid from the pump delivery line Ito thebraking circuit. The makeup valve means 230 comprises a valve body 260having a pair of spring pressed ball check valves 261 and 262. Fluid isconducted to the Before describing the operation of the system of Figs.

236 which is connected to the pressure conduit 212: and

' which opens into an internal annular inlet groove 237. Further, thevalve body is formed with a pair of pressure ports 238 and 239 connectedby a conduit 240 which may, if desired, be within the valve body 233.Motor ports 241 111.1142 lead from the valve bore, the former connectedf with the motor conduit118x for conducting fluid under pressure tothemotors to obtain forward operation, and fthe latterconnected to conduit117x for conducting fluid under pressure to the motors for reverseoperation. Drain ports 243 and 244 are connected by'a drain conduit 245which in turn leads to the inlet port 123x of the automatic 'braking'valve 29x; I

' The valve stem 2'35 is formed with a centrally disposed "land 247,spaced lands 248 and 249, and stem grooves check valves through aconduit 263. The check valve 261 delivers makeup fluid to a conduit 264and thence to the motor conduit 117x. The makeup valve 262 deliversfluid to a conduit 265 and thence to the motor conduit 118x.

During braking, when the motors 10 and 11 are rotated forwardly, fluidis drawn in through the conduit 118x and discharged through the conduit117x. Under jtheseconditions, the pressure of fluid in the conduit 117xmaintains the check valve 261 closed. In the event the braking circuitrequires makeup fluid, the reduced pressure in the conduit 118x issufficient to permit opening of .the check valve 262 by the pressure offluid in the conduit 263, to thereby deliver makeup fluid to the intakeline 118x. During braking operation, when the motors 10x and llx'tend torotate reversely, the check valve 262 will be held closed, and the checkvalve 261 will function to supplymakeup fluid.

. Makeup fluid is supplied to the makeup valve means 230 when the valvestem 235 is positioned in neutral through fpassages provided through thedirectional valve 18x.

The'makeup passages include the valve inlet port 236,

-the valve inlet groove 237, radial passages 266 in the valve stem 235,an axial passage 267 in the valve stem,

radial passages 268 in the valve stem, and the conduit 263.

Forward operation of the propelling motors is obtained by movement ofthe valve stem 235 to the right from the neutral center positionillustrated in Fig. 2 to the position illustrated in Fig.3. When thevalve stem is positioned rod is c'onnectedto the carburetor 1ever92x. isbiased to a "normal engine idle speed positionby :a

as illustrated in Fig. 3, the variable orifice 22x is opened to increasethe rate of flow through the pump delivery line 21x. Fluid flows throughthe valve inlet port 236, the adjustable orifice 22x, stem groove 250,valve outlet port 238, conduit 240, valve port 239, stern groove 251,and motor port 241 to conduit 118x to obtain forward operation of thepropelling motors.

At the same time, the pressure drop across the variable orifice 22x isreduced substantially, and the pressure of fluid in the conduit 240,through a conduit 270 is sufficient to cause movement of the pumpdisplacement control valve 23x to the position illustrated in Fig. 3,wherein pressure fluid flows through the valve 23x, through the overpressure relief-valve 24x and to the pump control conduit 67x toincrease the pump displacement in direct proportion to the flow ratethrough the adjustable orifice.

Also, fluid under pressure in the conduit 240 flows into a conduit 271to the upper end of the over pressure relief valve 24x so that in theevent of an excessively high pres sure rise in the system, the overpressure relief valve will operate as previously described to connectthe control conduit 67x to drain conduit 79x and reduce the pumpdisplacement.

Fluid under pressure from the conduit 240 also flows through the valvebody 233 to a conduit 272 and the port 145x in the automatic brakingvalve 29x to effect movement of the valve member 142x from the positionillustrated in Fig. 2 to the position illustrated in Fig. 3. 'In thelatter position, the stem groove 143x connects the drain ports 123x and124x to permit the flow of fluid from the propelling motors to drain.

I When the directional valve 18x and the adjustable orifice 22x areopened widely as illustrated in Fig. 3, the propelling motors x and 11xare operated at full speed in a forward direction with the various partsof the system positioned as illustrated in Fig. 3.

In the event that the propelling motors tend to overrun at a speedrequiring a greater flow than that provided by the pump, as, forexample, when the lift truck encounters a downward incline, the pressureof fluid in the pump delivery line 21x will drop due to the pumpingaction of the motors. A similar pressure drop occurs in the conduit 272,permitting the spring 144x in the automatic braking valve 29x to returnthe valve member 142x toward the position illustrated in Fig. 4. In thisposition, the valve member 142x functions to block the flow of fluidfrom the propelling motors to drain, thereby braking the motors down toa proper speed. Consequently, pressure in the pump delivery line 21xrises again to open the braking valve 29x.

If, during operation with the parts positioned as illustrated in Fig. 3,the lift truck encounters an upward incline, or an obstruction whichincreases the resistance of the motors to turn, there will occur aconsequent pressure rise in the pump delivery line 21x causing also apressure rise at the pressure port 167x of the torque valve 31x. Such apressure rise is efiective to cause movement of the torque'valve member161x from the position illustrated in Fig. 3 to the position illustratedin Fig. 5. In the latter position, the drain port 160x is blocked, andthe pressure port 158x is connected to the control port 159x, thusdelivering pressure fluid through the conduit 164x to shift the controlpistons and the swash plates in the propelling motors to a maximumdisplacement position providing 'a'niaximurn torque output and aconsequent reduction'in speed. The 'motors therefore respondautomatically to meet the increased resistance to turning.

At the same time, the speed of the prime mover 17x is also increased tomeet the increased demand. The engine speed is automatically increasedby the means 231 previously referred to in general. This means comprisesa piston and cylinder device including a cylinder 275 having a piston276reciprocable therein. The piston The piston spring 277. On the oppositeside of the piston-from the spring, the cylinder 275 is connected to thepump delivery line 21x by the conduit 278. Thus, when the pressure risesin the pump delivery line, the-piston is shifted against the bias of thespring to a position illustrated in Fig. 5 to increase the flow of fuelto the engine 17x thereby increasing the engine speed and pump speed tomeet the increased demand. After the obstruction or the ramp encounteredby the truck has been negotiated, pressure will drop in the pumpdelivery line 21x, and the parts returned to the position illustrated inFig. 3.

A particular advantage provided by the system of Figs. 2-5 is derived byincorporating the adjustable orifice 22x in the directional valve 18x ina manner so that both are controlled by the single operator lever 255 toopen and the same rate.

Modification of Fig. 6

The modified system illustrated in Fig. v6 is similar to thoseillustrated in Figs. 1 and 2 in that it incorporates an adjustableorifice for controlling the flow rate and a pump control for controllingthe pump displacement in a manner to provide a variable volume, variablepressure system which functions to delivery fluidonly at thepressure andflow rate required for a given operation. The system of Fig. 6 issimilar to that of Fig. 2 in that it includes only propelling motors 10yand 11y for connectionwith the driving wheels of a lift truck or thelike, without including motors for operating auxiliary equipment, thoughthe latter could be included if desired.

The principal advantage in the system of Fig. 6 .not provided in theother systems is embodied in the provision of a torque multiplying valvemeans including, in addition to an automatic torque valve, a manuallyoperable torque valve which may be utilized to hold the propellingmotors in maximum displacement, minimum speed operation to inch thevehicle along, thereby enabling exact speed control in close quartersregardless .of the condition of surface traversed by the vehicle.

In describing Fig. 6, parts which correspond to similar parts in thesystem of Fig. 1 .are designated .by similar reference numbers with asuffix y. The propelling motors lily and My may be identicalwith thereversible, variable displacement propelling motors 1t and .11 in thesystem of-Fig. 1. As illustrated in Fig. 6, themotorhousings includedrain conduits 280 and 281 respectively for conducting leakage fluidfrom the motor housings to the drain conduit 182y for return to thereservoir 16y.

Operating fluid under pressureissuppliedto the motors by a pump means15y which may, if desired, 'be identical with the variable speed,variable displacement pump 15 illustrated in .Fig. 1. As illustrated,however, the pump means15y of Fig. 6 takes theform of a double unit pumpwhich includes a first pump section 282 and a second pump section 283.The .double unit pump draws fluid from the reservoir 16y through aconduit 41y and vdelivers to a pump delivery conduit 21y. Pump 15y is ofthe variable displacement type in which the axially reciprocable pumpingpistons are controlled by variable angle swash plates 234and 285respectively. The swash plates are normally disposed in minimumdisplacement positions and may be moved to increased displacementpositions by a control piston 1286 reciprocable in a cylinder 287 whichmay be connected to drain or topressure fluid through a conduit 67y anda pump displacement control valve 233 which may be identical withthecontrol valve 23 in the system of Fig. l. The pump283 .is driven by adrive shaft 288 which may be connected wan prime mover similar to thatillustrated at 17 in Fig. l. The second pump section-may be connectedina conventional manner to drive the first pump section 282.

forms the variable orifice 22y. The directional valve 18y inthej systemof Fig. 6 is identical in most respects with the directional valve 18inthe system of Fig. l, and for this reason will not be described indetail. Operation of the directional valve 18y in the system of Fig. 6is obtained in a manner different from that employed in Fig. l in theuse of an operating lever 290 which is pivotally connected directly tothe valve stem of the directional valve and also pivotallyinterconnected with the valve stem of the means forming the orifice 22y.Operation or these two valves will be described more in detailprese'ntly;

Control over the displacement of the pump 15y is exercised by thecontrol valve 23y in a manner identical with the control exercised bythe valve 23 in Fig; 1. If desired, an over pressure relief valvesimilar to that illustrated at 24 and 24 in'Figs. 1 and '2 respectivelymay be utilized in a similar manner in the unit of Fig. 6. Thedirectional valve 18y'for controlling the flow of operating fluid to andfrom the propelling motors y and 11y, being identical with thedirectional valve 18 in the systeinof Fig. l, includes valving forbraking the propelling motors on slow down to a stop and when the truckis parked on an incline in neutral. Accordingly, thesystem of Fig. 6includes braking relief valve means 26y which is equivalent to thebraking valve means 26 in. the system of Fig. 1, and includes a brakingrelief valve138y for relieving the pressure of braking fluid in theconduit 117y and a braking relief valve 139 for relieving the pressureof braking fluid in the conduit 118 Also, the system of Fig. 6 includesan automatic valve means 293 which is identical with the brake valve 29in the system of Fig., l.

' The system of Fig. 6 incorporates an automatic torque multiplicationvalve 31y for controlling the displacement of'the propelling motorswhich is identical in operation with the torque valve 31 in the systemof Fig. 1. As illustrated in Fig. 6, however, the automatic torque valveis incorporated in a combined torque valve means 291 which alsoincorporates a manually controllable torque valve generally designated292.

The variable orifice 22y in the system of Fig. 6 is formed by meansincluding a valve body 295 which is formed with a valve bore having aslidable valve stem 296 formed with a centrally located valve land 297and stem grooves 298 and 299 on opposite sides of the land. The land 297is tapered at opposite ends and cooperates with a valve inlet groove 300to form the variable orifice 22y, The valve stem 296 is normally biasedby spring 301 to a neutral center position not illustrated wherein thevalve land 297 completely blocks the flow of fluid through the inletgroove 300. The valve stem 296 is movable by operation of the controllever 290 which may be utilized to move the valve stem in oppositedirections from the neutral center position to alternatively connect theinlet groove with an outlet port 302 through stem groove 299 or toconnect the inlet groove 300 to an outlet port 303 through stem groove298, the latter position being illustrated in Fig. 6. In either of thelast described two positions of the valve stem 296, the variable orifice22y may be opened by variable amounts to provide a variable flow ratethrough the orifice to the inlet ports of the directionalvalve 18y.

The springs provided for centering the valve stem 296 and thedirectional valve stem normally function to maintain the operating lever290 in a substantially upright positionnot illustrated. The operatinglever may be moved from the described neutral position to the right, asseen in Fig. 6, to the position illustrated to cause movement of thedirectional valve stem to a position for directing pressure fluid to themotor conduit 117y for. operating the propelling motors reversely. Inthis case, the valve stem 2 96 moves to the right from the neutralcenter position, and'the' directional valve stem moves to the left fromthe neutral center position. Alternatively, the opcrating lever 290 maybe moved to the left from the neutralcenter position described to causemovement of the valve stem 296 to the left from its neutral centerposition and to cause movement of the directionalvalve stem to' theright from its neutral center position to obtain the delivery ofpressure fluid to the motor conduit 118 fordriving the propelling motorsforwardly. In either of the orifice 22 only partly so as to obtain apartial flow rate to the motors 10 and 11 to obtain their operation at alow speed.

The manually controllable torque valve 292. includes a valve bore whichreceives a slidable valve stem 310 having a stem groove 311 normallypositioned to connect drain port 312 ad motor port 313, the latter beingcon nected to the motor port y in the automatic torque valve by apassage 314 so that the control pistons of the propelling motors areconnected to drain through stem groove 163y and drain port 1593 tocondition the propelling motors for minimum displacement. The valve stem310 is movable to the position illustrated in Fig. 6 .by an operatinglever 315 in which position the stem groove 311 connects the motorport313 to a pressure port 316. The pressure port 316 is connected by apassage 317 to a pressure port 158 in the automatic torque valve. Thus,when the manual torque valve stem is positioned as illustrated in Fig.6, the controljpistons of the propelling motors are connected topressure fluid through the conduit 16431, stem groove 1633 passage 314,stem groove 311, passage 317, port 15831, and pressure conduits 318 and320 to cause maximum displacement, low speed, maximum torque operationof the propelling motors un der manual control. I

The manually operable torque control valve 292 may be utilized to holdthe variable displacement propelling motors in full displacement,providing the lowest speed and maximum torque at the truck wheelsregardless of the load. This permits the vehicle to be inched along, andadditionally to roll over an obstruction without a re duction in speed,the increased load being evident only in a rise in system pressure.Thus, the operator is enabled to maintain exact speed control in closequarters regardless of the condition of the floor or terrain he istraveling over.

We claim:

1'; In a hydraulic system, at least one hydraulic motor adapted forconnection with a propelling wheel of a vehicle, at least one additionalhydraulic motor adapted for connection with auxiliaryvehicle equipment,a variable displacement pump having a discharge line for de-. liveringoperating fluid under pressure to the motors, a variable speed primemover for driving the pump, separate valves, one for "controllingthefloW-of operating fluid to each motor, a single control member, meansfor interconnecting the control member with the valves,the pump and theprime mover for controlling the operation of both valves, for varyingthe displacement of the pump, and for varying the speed ot'the primemover.

2. In a hydraulic system, at least one hydraulic motor adapted forconnection with a propelling wheel of a vehicle, atleast one additionalhydraulic motor adapted for 21 ing the pump displacement and the speedof the prime mover.

3. In a hydraulic system, at least one hydraulic motor adapted forconnection with a propelling wheel of a truck or the like, at least onehydraulic motor adapted for connection with auxiliary truck equipment,means providing a source of operating fluid under pressure, separatevalves, one for controlling the flow of operating fluid to each motor,each valve comprising a slidable valve stem, fluid operable means foreflecting movement of one valve stem, solenoid means for effectingmovement of the other valve stem, control valve means for controllingthe flow of pressure fluid to the fluid operable means, a manuallyoperable control member for actuating the control valve means, andswitch means on the control member connected in circuit with thesolenoid means for effecting operation of latter.

4. In a hydraulic system, at least one hydraulic motor adapted forconnection with a propelling wheel of a truck or the like, at least onehydraulic motor adapted for connection with auxiliary truck equipment,means providing a source of operating fluid under pressure, separatevalves, one for controlling the flow of operating fluid to each motor,each valve comprising a slidable valve stem, separate fluid operablemeans, one for effecting movement of each valve stem, separate controlvalve means, one for controlling operation of each fluid operable means,and a manually operable control member for actuating the control valvemeans either separately or simultaneously.

5. In a hydraulic system, at least one hydraulic motor adapted forconnection with a propelling wheel of a truck or the like, at least onehydraulic motor adapted for. connection with auxiliary truck equipment,means providing a source of operating fluid under pressure, separatevalves, onefor controlling the flow of operating fluid to each motor,each valve comprising a slidable valve stem, separate fluid operatablemeans, one for eflecting movement .of each valve stem, separate controlvalve means, one for controlling operation of each fluid opera ablemeans, and a manually operable control member movable in one directionfor actuating one control valve means and movable in another directionfor actuating the other control valve means.

6. In a hydraulic system, at least one first hydraulic motor adapted forconnection with a propelling wheel of a truck or the like, a secondhydraulic motor adapted for connection with a truck lift device or thelike extending and retracting the lift device, a third hydraulic motoradapted for connection with a truck lift device raising and lowering thelift device, means providing a source of operating fluid under pressure,separate directional valves respectively for controlling the flow ofoperating fluid to the first, second and third'm'otors, each of saidvalves comprising a movable valve stem, separate 'fluid operable means,one for efiectig movement of each of two valve stems, solenoid means foreflecting movement or the other valve stem, separate control valvemeans, one for controlling operation of each fluidoperable means, asingle manually operable control member for actuating both control valvemeans, and switch means on the control member connected in circuit withthe solenoid means for effecting operation of the latter.

7. In a hydraulic systernfor a lift truck or the like, a 'reversiblehydraulic motor, a pump forsupplying operating fluid under pressure, tothe motor, a directional valve -for controlling the flow of pressurefluid to the motor including a valve stem movable in opposite directionsfrom a neutral center'position to obtain-operation of the motor, inoppositedirection, fluid operable means, one for eflecting movement ofthe directional valve stem ineach direction from the center position,'control valves, one-for admitting fluid under pressure to each'fluidoperable' means, each control valve having a valve stem normallypositioned to connect the associated fluid oper- 22 able means to drainand movable to a position eonfleeting the associated fluid operablemeans to' pressure fluid, an elongated manually o erable control member:pivotally mounted at one end for pivotal movement in one direction froma neutral center position to actuate one control'valve stem and forpivotal movement in another direction from the neutral center actuatethe other control valve stem. V 1

8. In a hydraulic systemfor a lift truck or the like a reversiblehydraulic motor, a pump for supplying oper-' ating fluid under pressureto the motor, a variable speed prime mover for driving the pump, adirectional valve for controlling the flow of pressure fluid to themotor including a valve stem movable in opposite directions from aneutral center position to obtain operationof the motor in oppositedirections, fluid operable means, one for elfecti'ng movement of thedirectional valve stem in each direction from the center position,control valvcs, one for admitting fluid under pressure to each fluidoperable means, each control valve having avalve stem normallypositioned to connect the associated fluid operable means to drain andmovable to a position connect ing the associated fluid operable means topressure fluid, an elongated manually operable control member pivotallymounted at one end for pivotal movement in one 'di=- reason from. aneutral center position to actuate-one control valve stem and forpivotal movement in another direction from the neutral center positionto actuate the other control valve stem, means mounting the controlmember for rotation manually about its elongated axis, and meansconnected to the control member for varying the speed of the prime moveron rotation of the control member.

9. .In a, hydraulic system for a lifttruck 'or the like, a reversiblehydraulic motor, a variable displacement pump for supplying operatingfluid undenpressureto the motor, a directional valve for controllingthexflo'w of pressure fluid to the motor including a valve stem movablein opposite directions from a neutral center position to obtainoperation of the motor in opposite directions, fluid operable means, onefor eflecting movement-of the directional valve stem in each directionfrom'the center position, control-valves, one for admitting fluid'underpressure to each fluid operable'means, each control valve having a valve"stem normally positioned to connect the associated fluid operable meansto drain-and movable to a position connecting the associatedfluidoperable means to pressure fluid, an elongated manually operablecontrol member "pivotally mounted at one end for pivotal movement in onedirection from a neutral center position to actuate one control valvestem and for pivotal movement in another direction from the neutralcenter position toacfuate the other control valve-stem, means mountingthe control member for rotation manually about its elongated axis, andmeans connected to the control member for varying the pump displacementon rotation ofthecontrol member. v I

10. In a hydraulic system for a lift truck-or the like, a reversiblehydraulic motor, avaria bl'e displacement pump for supplying operatingfluid under pressure to the motor, a variable speed prime mover for''dr'iv'ing pump, a directional valve for controlling the new of pressurefluid to the motor including a valve stem f "vable in oppositedirections from a neutral center position to obtain operation of themotor in oppositedifections,

fluid operable means, one for effecting movemenfof the directional valvestem in each direction from the center position, control valves, one foradmitting "fluid under pressure to each fluid operable means, eachcontrol valve having a valve stem normally positioned to connect theassociated fluid operable means to drain and movable to *a positionconnecting the associated *fliiid operable means to pressure fluid, anelongated. manually operable control member-pivotally mounted at one endfor pivotal movement in one direction from a neutral center position toposition to actuate one control valve stem and for pivotal movement inanother direction from the neutral center position to actuate the othercontrol valve stem, means mounting the control member for rotationmanually about its elongated axis, and means connected with the controlmember for varying the speed of the prime mover and for varying the pumpdisplacement on rotation of the control member.

- 11. In a hydraulic system for a lift truck or the like, a pair .ofreversible hydraulic motors, a pump for supplying operating fluid underpressure to the motors, a pair of. directional, valves, one forcontrolling the flow ofopcrating fluid to each motor, each valveincluding a directional valve stem movable in opposite direction from a.neutral center position to obtain operation of the associated motor inopposite directions, fluid operablemeans, one for etfecting movement ofone directional valve stem in each of the opposite directions, controlvalves, one for admitting fluid under pressure to eachfluidoperable'means, each control valve having a valve stem normallypositioned to connect the associated fluid operable means to drain andmovable to a position connecting the associated fluid operable means topressurefluid, an elongated, manually operable control member pivotallymounted at one end for pivotal movement in one direction from a neutralcenter position to actuate one control valve stem and for pivotalmovement in another direction from the neutral center position toactuate the other control valve stem, a pair of solenoids, one foreffecting movement of the other directional valve stem in each of theopposite directions, and switch means on the manually operable controlmember connected in circuit with said solenoids and operable to energizeeither solenoid.

=12. In a hydraulic system having a pair of directional valves, eachincluding a directional valve member movablein opposite directions froma neutral center position, fluid operable means, one for effectingmovement of each directional valve stem, a pair of control valve means,one for each fluid operable means, each control valve means comprising apair of control valves, one for obtaining movement of the associatedfluid operable means in each direction, each of said control valvesincluding a control valve stem normally positioned to connect theassociated fluid operable means to. drain and movable to a positionconnecting the fluid operable means to pressure fluid, a manuallyoperable control member universally mounted at oneend for pivotalmovement in any direction from a neutral center position, said controlvalves being arranged about the axis of the control member with thestems of the control valves spaced at ninety degree intervals and withthe stems of each control valve means at diametrically oppositepositions for actuation respectively on pivotal movement of the controlmember in opposite directions, the control member being movable indirections intermediate said opposite directions for effectingsimultaneous actuation of any two, adjacent control valve stems,

, 13. In a hydraulic system for a lift truck or the like,

a hydraulicmotor, a pump for supplying operating fluid under pressureto. the motor, passage means connecting -'the motor inlet'and the pumpoutlet, a valve in the passage means for-controlling the rate of flow ofpressure .fluid from the pump to the motor, and means in fluidcommunication with the passage means for sensing the rate of flowtherethrough and controlling the pump to vary the pump output withvariations in the demand as determined by operation of the valve therebyto provide delivery of the fluid at the rate and pressure required for agiven operating condition.

14. The combination of claim 13, wherein the means for controllingthe'pump comprises, means for varying the pump displacement, andincluding means interconnecting the sensing means and the displacementvarying means to increase the pump displacement in response to 24increase in the flow rate and to decrease. the pump dis-' placement inresponse to decrease in the flow rate. 7

15. In a hydraulic system, a hydraulic motor adapted for connection witha propelling wheel of a truck or the like, a variable displacement pumpfor supplying operating fluid under pressure to the motor, passage meansconnecting the pump outlet to the motor inlet, a valve in the passagemeans for controlling the flow of pressure fluid from the pump to themotor, an orifice of variable size in the passage means between the pumpand the motor, means for varying the size of the orifice opening to varythe rate of flow therethrough, means for varying the pump displacement,and means in fluid communication with the passage means for sensing thepressure drop across the orifice and controlling the displacementvarying means to increase the pump displacement in response to decreasesin pressure drop across the orifice and to increase the pumpdisplacement in response to increases in pressure drop across theorifice.

16, The combination of claim 15, including a single control member foroperating the valve for the motor and for varying the size of theorifice opening.

17. The combination of claim 15, including means for simultaneouslyopening the valve and increasing the size of the variable orificeopening. v

18. In a hydraulic system, a hydraulic motor adapted for connection witha propelling wheel of a truck or the like, a variable displacement pumphaving a discharge line for supplying'operating fluid under pressurefrom the pump to the motor, a directional valve for controlling the flowof pressure fluid from the pump to the motor, an orifice of variablesize in the pump discharge line between the pump and the valve, meansfor varying the size of the orifice opening as the demand on the systemvaries, fluid operable meansfor varying the pump displacement, meansnormally biasing the displacement varyingmeans to a minimum displacementposition, a control valve for con trolling the flow of fluid to and fromthe displacement varying means, said control valve being responsive toincreases in pressure drop across the orifice to connect thedisplacement varying means to drain to thereby decrease pumpdisplacement, and being responsive to decreases in pressure drop acrossthe orifices to connect the displacement varying means to pressure fluidto thereby increase pumpdisplacement.

19. The combination of claim 18, including an over pressure relief valveconnected between said control valve and the displacement varying meansnormally positioned to permit the flow of fluid between the controlvalve and the displacement varying means, said over pressure reliefvalve being responsive to predetermined excessively high pressure in thepump discharge line between said orifice and the directional valve toconnect the displacement varying means to drain. i

20. In a hydraulic system, a hydraulic motor adapted for connection witha propelling wheel of a truck or the like, a variable displacement pumphaving a delivery line for supplying operating fluid under pressure, adirectional valve for controlling the flow of pressure fluid from thedelivery line to the motor, an orifice of adjustable size in the pumpdelivery line between the pump and the directional valve, means forvarying the size of the adjustable orifice to vary the rate of flow fromthe pump to the valve, a common actuator for the directional valve andtor the orifice adjusting means operable to open and close thedirectional valve to permit and prevent the flow of pressure fluid fromthe pump to the motor and operable to increase and decrease the orificesize to control the rate of flow to the directional valve, and meansresponsive to the pressure drop across the adjustable orifice toincrease the pump displacementon decreases in said pres-sure drop whenthe orifice size is increased to increase the flow rate and to decreasethe pump displacement onincreases in said pressure drop when the orificesize is decreased to decrease the flow rate.

th n,

'21. The combination or claim renaming nee-fie for varying thedisplacement of the motor normallydisposed in a displacemenflhigh speed,low torque position, and means for sensing the load on the motor, tomove the displacement varying, means to increase the motor displacementto a low speed, high torque value in response to increases in theload onthe motor.

22. The combination of claim 20, including fluid o erable means forvarying the displacement of the motor, normally disposed in a minimumdisplacement, high speed, low torque position, torque valvemeans'normally positioned to connect the fluid operable motordisplacement varying means to'drain and operable to connect the fluidoperable motor displacementvarying means topressure fluid to effectmovementthereof to a maximum displacement, low speed, hightorque'position,

23. The'combination ofclair'n 22, whereinthetorque valve means comprisesa manually operable valve movable from a normal position to a positionfor delivering pressure fluid from the pump discharge line to-the fluidoperable motor displacement varying means, said torque valve beingmanually operable at will to increase or decrease the speed of the motorand simultaneously vary the torque outputof the motor inverselyt 24. Thecombination of claim 22, wherein the torque valve means comprises avalvenormally biased'to aposition connecting the fluidoperable motordisplacement varying means to drain and responsive to increased pressurein the pump delivery line as a result of increased resistance of themotor to turn, to connect the displacement varying means 'to the pumpdelivery line to cause movement of the displacement varyingnieans to ,amaximum displacement, low speed, high torque position,

25. The combination of claim 20, including braking valving on saiddirectional valve positionable 'torestrict the flow of fluid from themotor when the directional valve is positioned to block the flow offluid from the pump to the motor, thereby to brake the truck on slowdownand when parked on an incline.

26. The combination of claim 20, including a braking valve subjected topressure fluid in the pump delivery line and positioned thereby toconnect the motor outlet to drain, means biasing the braking valve to aposition restricting the flow of fluid from the motor to drain, saidbraking valve being operable by said biasing means, upon a drop inpressure of fluid in the pump delivery line whenever the motor tends tooverrun at a speed requiring more flow than that provided by the pump,to restrict the flow of fluid from the motor to brake the truck.

27. In a hydraulic system, a hydraulic motor adapted for connection witha propelling wheel of a truck or the like, a variable displacement pumphaving a delivery linefor supplying operating fluid under pressure, adirectional valve for controlling the flow of pressure fluid from thedelivery line to the motor, fluid operable means for eifecting operationof the directional valve, a control valve for controlling the operationof the fluid operable means, means forming an orifice of adjustable sizein the pump delivery line between the pump and the directional valveincluding an annular valve seat and a needle valve member threadablymounted for adjustment relative to the annular valve seat to vary thesize of the orifice to vary the rate of flow from the pump to thedirectional valve, a manually operable control member pivotally mountedat one end for pivotal movement to actuate said control valve, meansmounting the control member for rotation manually about its axis, meansconnecting the control member and the needle valve member to adjust thelatter relative to the annular valve seat on rotation of the controlmember, and means responsive to the pressure drop across the adjustableorifice to vary the pump displacement directly With variations in theflow rate through the orifice.

28. In a hydraulic system, a hydraulic motor adapted for connection witha propelling Wheel of a truck or the sis? for supplying operatingfluidunder pressure, a irectional valve for controlling the flow of 'pressurefluidtromfthe delivery line to the motor, including reciprocal directiona1 valve movablein opposite directions from aneutr'al center position,means forming an adjustable orifioe in the pump delivery line betweenthe pump'an'd the directional valve including a control valve membermovable in opposite directions from a neutral center position forvarying the size of the adjustable oritice to vary the rate of flow fromthe pump to the directional valve, a manually operable actuatorpivotally connected -to both valve member and pivotable in oppositedirections non neutral center position to move the directional valve m mr i 'b po e d ec o "and. wed the s e if t e adj bl br fi e, nd. e n rponsive to *3 p e s drop across the "adjustable orificeto vary th; pumpdis;- placement directly with variations in the new rate throughtheorifice. I '29. In a hydraulic system; a hydraulic motor adapted foconnection with a propelling wheel of a truck or the like, a variabledisplacement pump having a delivery line forsupplying operating fluidunder pressure, directional valve means including a valve stem movablein opposite directions from a neutral center position and having valvingthereon for controlling the flow of pressure fluid from the deliveryline to the motor, means forming an orifice of adjustable size inth'epump delivery line between the pump and said valving includingadditional valving' onsaid stem. movable with said stem for varyingthe'size of the adjustable orifice to vary the rateo f 'flo'vv from thepom-pr the motor,.means ,for effecting movement of and means responsivetothe pressure drop the valve ste v, aqm sthe. d u ab e r f v ry he u pd r fi ment directly with variations in the flow rate through theorifice.

30. In a hydraulic system, a hydraulic motor adapted for connection witha propelling wheel of a truck or the like, a hydraulic motor adapted forconnection with auxiliary truck equipment, a pump for supplyingoperating fluid under pressure, a variable speed prime mover for drivingthe pump, separate valves one for controlling the flow of operatingfluid to each motor, each valve having a movable valve member, separatefluid operable means one for effecting movement of each movable valvemember, separate control valve means one for controlling operation ofeach fluid operable means, a pivoted control lever selectively movablein one direction for actuating one control valve means and in anotherdirection for actuating the other control valve means, means mountingthe control lever for rotation about its elongated axis, and means forvarying the speed of the prime mover on rotation of the control member.

31. In a hydraulic system, a hydraulic motor adapted for connection witha propelling Wheel of a truck or the like, a hydraulic motor adapted forconnection with auxiliary truck equipment, a variable displacement pumpfor supplying operating fluid under pressure, separate valves one forcontrolling the flow of operating fluid to each motor, each valve havinga movable valve member, sep-' arate fluid operable means one foreffecting movement of each movable valve member, separate control valvemeans one for controlling operation of each fluid operable means, apivoted control member selectively movable in one direction foractuating one control valve means and in another direction for actuatingthe other control valve means, means mounting the control member forrotation about its elongated axis, and means for varying the pumpdisplacement on rotation of the control member.

32. In a hydraulic system, at least one hydraulic motor adapted forconnection with a propelling wheel of a vehicle, at least one additionalhydraulic motor adapted for connection with auxiliary vehicle equipment,a pump in fluid communication with the motors for delivering operatingfluid under pressure thereto, a variable speed new prime moverfordriving the pump, separate directional valves, one fol-controlling theflow of operating fluid to each motor, a single elongate control membermounted for universal pivotal movement and for rotation about itselongate axis separately or simultaneously, and means forinterconnecting the control member with the valves and the prime moverfor effecting operation of both valves either. separately orsimultaneously on pivotal movement of the member and for varying thespeed of the prime mover on rotation of the member. 33. In a hydraulicsystem, at least one hydraulic motor adapted for connection with apropelling wheel of a vehicle, at least one additional hydraulic motoradapted for connection with auxiliary vehicle equipment, a variabledisplacement pump having a discharge line for deliv' eringoperatingfluid under pressure to the motors, separate reversing directionalvalves, one for controlling the flow of operating fluid to each motor, asingle control member mounted for universal pivotal movement and forrotation about its elongate axis separately or simultaneously, and meansfor interconnecting the control member with the valves and the pump' foretfecting operation of both valves either separately or simultaneouslyand in either direction on pivotal movement of the member andfor varyingthe displacement of the pump on rotation of the member. 7 34. In ahydraulic system for mobileequipment, a hydraulic motor, a pump in fluidcommunication with the motor for delivering operating fluid underpressure thereto, a variable speed prime mover for driving the pump avalve for controlling the flow of, operating fluid to the motor, asingle elongate control member mounted for rotary movement about itselongate axis and for pivotal movement separately or simultaneouslyabout an axis transverse to the rotary axis, and means interconnectingthe control member with the valve and the prime mover for effectingoperation of the valve on one of said member movements and for 'varyingthe speed of the prime mover on the other of said movements. 7

35. In a hydraulic system for mobile equipment, a hydraulic motor, avariable displacement pump in fluid cornmunication with the motor forsupplying operating fluid under pressure thereto, a reversingdirectional valve for controlling the flow of operating fluid to themotor, andfa single elongate control member mounted for rotary movementabout its elongate axis and for pivotal movement separately orsimultaneously about an axis transverseto the rotary axis, and meansinterconnecting the control member vw'th the valve and the pump foreffecting operation of the valve in either direction on'one of saidmember movements and for varying the displacement of the pump on theother of said member movements.

References Cited in the file of this patent UNITED STATES PATENTS2,774,436 Ferris Dec. 18, 1956

